java单例

//枚举模式
public enum  EnumSingle {
    INSANCE;
    public void doSomeThing(){
        System.out.println("do some thing");
    }
}

package my;


//双检查
public class Single {
    private Single(){}

    private  volatile static Single instance = null;

    public static Single getInstance(){
        if(instance == null){
            synchronized (Single.class){
                if(instance == null){
                    instance = new Single();
                }
            }
        }
        return instance;
    }

}

package my;


//饿汉式
public class Single1 {
    private static Single1 instance = new Single1();

    private Single1(){}

    public static Single1 getInstance(){
        return instance;
    }

}

package my;


//懒汉式
public class Single2 {
    private static Single2 instance = null;

    private Single2(){};


    private static Single2 getInstance(){
        if(instance == null)
            instance = new Single2();
        return instance;
    }
}

package my;


//静态内部类
public class Single3 {
    private Single3(){}

    private static class Single3Hold{
        private static Single3 istance = new Single3();
    }

    public static Single3 getInstance(){
        return Single3Hold.istance;
    }
}